Method and apparatus for transmitting and receiving reference signal in wireless communication system

ABSTRACT

Methods and apparatus are provided for transmitting processing reference signals in a mobile communication system. A base station determines a reference signal pattern comprising at least one resource element, generates a bitmap indicator indicating whether zero transmission power is assigned to the at least one resource element of the reference signal pattern, and transmits the reference signal pattern and the bitmap indicator to a terminal. The terminal receives the reference signal pattern and the bitmap indicator, and processes a reference signal extracted according to the reference signal pattern and the bitmap indicator.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to anapplication filed in the Korean Intellectual Property Office on Aug. 13,2010, and assigned Serial No. 10-2010-0078232, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a cellular radiocommunication system, and more particularly, to a method in which atransmitter informs a receiver of a reference signal pattern that is tobe muted in a system.

2. Description of the Related Art

Mobile communication systems have evolved into high-speed, high-qualitywireless packet data communication systems that provide data servicesand multimedia services that far exceed the early voice-orientedservices. Various mobile communication standards have been developed tosupport services of the high-speed, high-quality wireless packet datacommunication systems. These standards include High Speed DownlinkPacket Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), bothdefined in 3^(rd) Generation Partnership Project (3GPP), High RatePacket Data (HRPD) defined in 3^(rd) Generation Partnership Project-2(3GPP2), and 802.16 defined in Institue of Electrical and ElectronicEngineers (IEEE).

The existing 3^(rd) generation wireless packet data communicationsystems, such as HSDPA, HSUPA and HRPD, use specific technologies, suchas an Adaptive Modulation and Coding (AMC) method and aChannel-Sensitive Scheduling (CSS) method, to improve transmissionefficiency. Through the use of the AMC method, a transmitter can adjustan amount of transmission data according to a channel state.Specifically, when the channel state is not ‘Good’, the transmitterreduces the amount of transmission data to adjust a reception errorprobability to a desired level. When the channel state is ‘Good’, thetransmitter increases the amount of transmission data to adjust thereception error probability to the desired level, thereby efficientlytransmitting a large volume of information. Through the use of a CSS-based resource management method, the transmitter selectively servicesa user having a channel state that is better than those of other users.This selective servicing provides an increase in system capacity whencompared to a method of allocating a channel to one user and servicingthe user with the allocated channel. Such a capacity increase isreferred to as ‘multi-user diversity gain’. Thus, the AMC method and theCSS method each apply an appropriate modulation and coding scheme at themost-efficient time, which is determined based on partial channel stateinformation that is fed back from a receiver.

Research has been conducted in order to replace Code Division MultipleAccess (CDMA), the multiple access scheme used in the 2^(nd) and 3^(rd)generation mobile communication systems, with Orthogonal FrequencyDivision Multiple Access (OFDMA) in the next generation system. 3GPP and3GPP2 have begun standardization of evolved systems employing OFDMA. TheOFDMA scheme results in a capacity increase when compared to the CDMAscheme. One reason for the capacity increase in the OFDMA scheme is thatthe OFDMA scheme can perform scheduling in the frequency domain(frequency domain scheduling). While the transceiver acquires capacitygain according to a time-varying channel characteristic using the CSSmethod, the transceiver can obtain a higher capacity gain through theuse of a frequency-varying channel characteristic.

In order to increase the capacity gain using the aforementioned methods,information on the radio channel condition is required. The moreaccurate the radio channel condition information the greater thecapacity gain. When measuring the radio channel condition based on areference signal, the accuracy of the measurement increases as theSignal-to-Interference plus Noise Ratio (SINR) of the received referenceincreases. Accordingly, in order to increase the accuracy of the channelcondition information, the power of the interference on the receivedreference signal must be reduced. Muting is one method that reduces theinterference. Muting empties a time resource, a frequency resource, anantenna resource, or a code resource used by other transmitters totransmit their reference signals.

In order gain the advantages provided by muting, the transmitter shouldnotify the receiver of the Resource Elements (REs) at which thereference signal is muted. In a 3GPP Long Term Evolution (LTE) system,for example, there are not a large number of reference signal patternsbecause the reference signal pattern is determined based on the Cell ID.In an LTE-Advanced (LTE-A) system, however, up to 20 reference signalpatterns can be used per antenna port and multiple reference signalpatterns can be muted regardless of the transmission of the referencesignals.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides a method for informing the receiver of the reference pattern tobe muted in a system, such as LTE-A, in which the number of referencesignal patterns varies depending on the antenna port.

According to an aspect of the present invention, a method is providedfor transmitting a reference signal of a base station in a mobilecommunication system. A reference signal pattern having at least oneresource element is determined at the base station. A bitmap indicatorindicating whether zero transmission power is assigned to the at leastone resource element of the reference signal pattern is generated at thebase station. The reference signal pattern and bitmap indicator aretransmitted from the base station to a terminal.

According to another aspect of the present invention, a base station isprovided for transmitting reference signals in a mobile communicationsystem. The base station includes a reference signal pattern determinerthat determines a reference signal pattern having at least one resourceelement. The base station also includes a reference signal patternmuting determiner that generates a bitmap indicator indicating whetherzero transmission power is assigned to the at least one resource elementof the reference signal pattern. The base station further includes atransceiver that transmits the reference signal pattern and the bitmapindicator to a terminal.

According to an additional aspect of the present invention, a method isprovided for processing reference signals transmitted by a base stationin a mobile communication system. A terminal receives a reference signalpattern having at least one resource element from the base station. Abitmap indicator, indicating whether zero transmission power is assignedto the at least one resource element of the reference signal pattern, isreceived. The reference signal extracted according to the referencesignal pattern and the bitmap indicator is processed.

According to a further aspect of the present invention, a terminal isprovided that processes reference signals transmitted by a base stationin a mobile communication system. The terminal includes a transceiverthat communicates signals with the base station. The terminal alsoincludes a controller that controls the transceiver to receive areference signal pattern having at least one resource element and abitmap indicator indicating whether zero transmission power is assignedto the at least one resource element of the reference signal pattern,and that processes the reference signal extracted according to thereference signal pattern and the bitmap indicator.

According to another aspect of the present invention, a system isprovided for transmitting and processing reference signals in a mobilecommunication system. The system includes a base station that determinesa reference signal pattern comprising at least one resource element,generates a bitmap indicator indicating whether zero transmission poweris assigned to the at least one resource element of the reference signalpattern, and transmits the reference signal pattern and the bitmapindicator to a terminal. The system also includes the terminal thatreceives the reference signal pattern and the bitmap indicator, andprocesses a reference signal extracted according to the reference signalpattern and the bitmap indicator.

According to an additional aspect of the present invention, an articleof manufacture is provided for transmitting a reference signal of a basestation in a mobile communication system, having a machine readablemedium containing one or more programs which when executed implement thesteps of: determining, at the base station, a reference signal patterncomprising at least one resource element; generating, at the basestation, a bitmap indicator indicating whether zero transmission poweris assigned to the at least one resource element of the reference signalpattern; and transmitting the reference signal pattern and bitmapindicator from the base station to a terminal.

Additionally, according to a further aspect of the present invention, anarticle of manufacture is provided for processing reference signalstransmitted by a base station in a mobile communication system, having amachine readable medium containing one or more programs which whenexecuted implement the steps of: receiving, at a terminal, a referencesignal pattern from the base station, wherein the reference signalpattern comprises at least one resource element from the base station;receiving a bitmap indicator indicating whether zero transmission poweris assigned to the at least one resource element of the reference signalpattern; and processing a reference signal extracted according to thereference signal pattern and the bitmap indicator.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram illustrating a Channel State Information ReferenceSignal (CSI-RS) pattern for use in an LTE-A system, according to anembodiment of the present invention;

FIG. 2 is a diagram illustrating pattern ID assignment to the CSI-RSpattern for use in an LTE-A, according to an embodiment of the presentinvention;

FIG. 3 is a diagram illustrating a tree structure for use in a mutingpattern notification method, according to an embodiment of the presentinvention;

FIG. 4 is a flowchart illustrating a muting pattern notificationmethodology, according to an embodiment of the present invention;

FIG. 5 is a block diagram illustrating a configuration of a transmitter,according to an embodiment of the present invention; and

FIG. 6 is a block diagram illustrating a configuration of a receiver,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. It should be noted that similarcomponents are designated by similar reference numerals although theyare illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

The terms utilized in the description are defined based on thefunctionality of the embodiments of the present invention, and may varyaccording to the intention of a user or an operator, usage, etc.Therefore, the definitions should be made based on the overall contentof the present specification.

In the following description, muting refers to a technique for emptingthe time, frequency, antenna, or code resources through which a neighbortransmitter transmits reference signals. Thus, muting a resource meanssetting a transmit power to zero for that resource.

If the resource is used, the transmission power is not zero for thatresource. Accordingly, if the resource is not muted, a non-zerotransmission power is assigned to that resource.

Although a description of embodiments of the present invention isprovided with reference to the OFDM-based mobile communication system,by way of example, it will be understood by those skilled in the artthat the embodiments of the present invention can be applied to othercommunication systems having similar technical backgrounds and channelformats, with a slight modification, without departing from the spiritand scope of the present invention.

In a first embodiment of the present invention, a transmitter notifies areceiver of muting with fixed RE granularity signaling. Since muting canbe applied to a plurality of reference signal patterns, the number ofbits required for the transmitter to notify the receiver of muting isequal to the number of cases of muting.

FIG. 1 is a diagram illustrating Channel Station Information ReferenceSignal (CSI-RS) pattern in an LTE-A system. Parts (a), (b), (c), and (d)of FIG. 1 show the CSI-RS transmission patterns for the cases that thetransmitter and the receiver use 2, 4, and 8 antenna ports, and TDD,respectively.

In case that 2 antenna ports are used as shown in part (a) of FIG. 1,the CSI-RS is transmitted in pairs of 0 and 1 allocated to the resourceelements having the same shape. In case of part (b) of FIG. 1 in which 4antenna ports are used, the CSI-RS is transmitted in pairs of 0, 1, 2and 3 allocated to the resource elements having the same shape. In caseof part (c) of FIG. 1 in which 4 antenna ports are used, the CSI-RS istransmitted in pairs of 0, 1, 2, 3 and 4, 5, 6, and 7. In part (d) ofFIG. 1, the CSI-RS is transmitted certain resource elements in the8^(th) and 10^(th) symbols.

It is noted that the resource elements paired to transmit the CSI-RS canbe allocated a pattern ID, e.g., P1 and P2 as depicted in FIG. 2.

The reference signal pattern, as shown in FIG. 1, is transmitted onfixed RE positions. However, the number of REs constituting a referencesignal pattern varies according to the number of antenna ports. In orderto maximize the granularity, it is effective to notify of muting inunits of RE. In this case, at least two REs are assigned for thereference signal of the serving cell. If REs are assigned, non-zerotransmission power is assigned to the corresponding Res. Two REs arerequired for transmitting a minimum reference signal with which the UserEquipment (UE) can measure the radio channel condition of the servingcell. Accordingly, in order to notify of muting in the highestgranularity, a total 38 bits is required. The number of bits requiredfor the notification of muting varies. Table 1 shows the numbers of bitsrequired for different RE granularities in the muting scheme, accordingto an embodiment of the present invention.

TABLE 1 RE granularity bits required for notifying of muting 1 40 (b₀,b₁, b₂, . . . , b₃₉) 2 20 (b₀, b₁, b₂, . . . , b₁₉) 4 10 (b₀, b₁, b₂, .. . , b₉) 8  5 (b₀, b₁, b₂, b₃, b₄) TDD only  3 (b₀, b₁, b₂)

In Table 1, one bit represents an RE of the corresponding granularityand indicates whether the corresponding RE is muted. Specifically, eachbit indicates whether the transmission power of the corresponding RE isset to 0. For example, if the RE granularity is 2, one of the referencesignal patterns available for two antenna ports in FIG. 2 is muted usingone bit. More specifically, assuming that b_(o), b₁, b₂, . . . , b₁₉ aremuting indicators, each individual bit indicates whether the referencesignal patterns P0 to P19 of FIG. 2 are used. For example, if b₀=1 (or0), the pattern P0 is muted. In this manner, the muting indicators ofthe embodiments of the present invention are expressed in the form ofbitmap. Accordingly, the terms ‘muting indicator’ and ‘bitmap indicator’are interchangeably used in the following description of embodiments ofthe present invention.

Table 1 shows a case where the number of antenna ports to the referencesignals of the serving cell is equal to the RE granularity for notifyingof muting.

However, the number of antenna ports to the reference signals of theserving cell may differ from the RE granularity for notifying of muting.If the number of antenna ports to the reference signals is less than theRE granularity, a reference signal pattern carrying reference signalsmay be muted. In this case, the REs to be muted are partially muted,with the exception of the reference signals of the serving cell.Specifically, the RE carrying the reference signal of the serving cellis not assigned a transmission power set to 0.

Referring to FIG. 2, it is assumed that the serving cell has two antennaports and uses the reference signal pattern P0. If the RE granularityfor muting is 4, the muting application is notified in consideration of4 antenna ports. If the transmitter provides a muting indicator forpattern P0, the receiver recognizes the situation as if the referencesignals are transmitted in all REs of pattern P0 when there are twoantenna ports, and two REs not carrying the reference signals are mutedin pattern P0 when there are four antenna ports.

In addition to the muting method provided in Table 1, another mutingmethod is provided with diverse RE granularities as shown in Table 2.

TABLE 2 RE granularity bits required for notifying of muting 1 38 (b₀,b₁, b₂, . . . , b₃₇) 2 19 (b₀, b₁, b₂, . . . , b₁₈) 4  9 (b₀, b₁, b₂, .. . , b₈) 8  4 (b₀, b₁, b₂, b₃) TDD only  2 (b₀, b₁)

Unlike Table 1, Table 2 shows muting indicators in which the part usedfor transmitting the reference signal is omitted from individualpatterns. For example, when the RE granularity is 8 and the referencesignal pattern P1 is used, the muting pattern indicators are interpretedas shown in Table 3, where all the patterns, excluding those carryingreference signals, are linked in order.

TABLE 3 Muting indicator Corresponding reference signal pattern b0 P0 b1P2 b2 P3 b3 P4

When compared with Table 1, the number of bits in Table 2 can be reducedby as many as 1 bit or 2 bits. When the RE granularity is 1 in Table 2,2 bits are saved. This is because the least number of REs are used forthe reference signal when the number of antenna ports is 2.

In the Table 3, the number of antenna ports to the reference signals isequal to the RE granularity of the muting indicator, however, the REgranularity of the muting indicator can greater than the number ofantenna ports. In this case, the patterns, excluding the patternincluding the reference signals of the serving cell, are mapped to themuting indicators in order. Table 4 shows an embodiment in which thepattern P1 is used in the case of an RE granularity of 8 and 4 antennaports.

TABLE 4 Muting indicator Corresponding reference signal pattern b0 P0 b1P2 b2 P3 b3 P4

When the number of antenna ports is 4, the pattern P1 includes thepattern P0 for when the number of antenna ports is 8, such that thereference signal patterns, except for the pattern P0, are mapped to themuting indicator.

An embodiment of the present invention relating to the muting patternnotification method with fixed RE granularities has been describedabove. A second embodiment of the present invention relating to a treestructure based notification is described in detail below.

Considering the reference signal patterns of FIG. 1, another embodimentof the present invention proposes a method for notifying of the mutingpattern using a tree structure, in that the patterns for cases having alarge number of antenna ports include patterns for cases having a smallnumber of antenna ports.

The reference signal patterns of FIGS. 1 and 2 show that the referencesignal patterns for cases having a small number of antenna ports aregathered into the reference signal patterns for cases having a largenumber of antenna ports. For example, in FIG. 2, the reference signalpattern P0 for the 8 antenna ports is formed by arranging the referencesignals patterns P0, P1, P2, and P3 for the 2 antenna ports. Thisstructure can be expressed in the form of a tree as shown in FIG. 3,according to an embodiment of the present invention.

Using the tree structure, the muting pattern notification scheme can bedetermined as described below.

A bitmap can be configured by allocating one bit to each node, as shownin FIG. 3. For example, all cases can be classified according to thenumber of antenna ports, such that the bitmaps for the cases of twoantenna ports and four antenna ports case. This results in the samemethod as described above with respect to the muting patternnotification method with fixed RE granularities.

When allocating one codeword per node, since the total number of nodesis 35, 6 bits are need to identify a node with a codeword, as shown inTable 5 below.

TABLE 5 Muting indicator (b0, b1, b2, b3, b4, b5) Corresponding node000000 P0 for 8 antenna ports 000001 P1 for 8 antenna ports 000010 P2for 8 antenna ports 000011 P3 for 8 antenna ports 000100 P4 for 8antenna ports 000101 P0 for 8 antenna ports 000110 P1 for 8 antennaports — — — — — — 100001 P18 for 2 antenna ports 100010 P19 for 2antenna ports

Since only one node can be designated, the degree of freedom for mutingpattern notification decreases as compared to the methods describedabove.

However, unlike the above-described methods, one codeword can beallocated to one node when the number of antenna ports is 8 or 4.Specifically, the muting pattern can be notified using 4 bits as shownin Table 6.

TABLE 6 Muting indicator (b₀, b₁, b₂, b₃) Corresponding node 0000 P0 for8 antenna ports 0001 P1 for 8 antenna ports 0010 P2 for 8 antenna ports0011 P3 for 8 antenna ports 0100 P4 for 8 antenna ports 0101 P0 for 8antenna ports 0110 P1 for 8 antenna ports — — — — — — 1101 P8 for 4antenna ports 1110 P9 for 4 antenna ports

Similarly, one codeword can be allocated to one node when the number ofantenna ports is 8. Specifically, the muting pattern can be notifiedusing 3 bits as shown in Table 7.

TABLE 7 Muting indicator (b0, b1, b2) Corresponding node 000 P0 for 8antenna ports 001 P1 for 8 antenna ports 010 P2 for 8 antenna ports 011P3 for 8 antenna ports 100 P4 for 8 antenna ports

If a muting indicator indicating a certain node is transmitted to the UEin the above-described embodiment, the reference signal pattern of thecorresponding node is muted.

Referring again to FIG. 1, the CSI-RS collides with Rel-8 dedicatedreference signal of port 5 in (a), (b), and (c), and collides with theRel-8 Common Reference Signals (CRSs) of ports 2 and 3. Accordingly,embodiments of the present invention provide the following rules to mutewhen the Rel-8 dedicated reference signal and CRS are colliding with theCSI-RS to be muted.

If it is necessary to mute a signal at positions where the Rel-8 CRS ordedicated reference signal is transmitted, the reference signals aremuted.

If the Rel-8 CRS for ports 3 and 4 are transmitted at certain REpositions in the reference signal pattern to be muted, the Rel-8 CRSsfor ports 3 and 4 are transmitted while muting at the remaining REpositions.

If the Rel-8 dedicated reference signal for port 5 is transmitted at theRE position of the reference signal pattern to be muted, the Rel-8dedicated reference signal for port 5 in transmitted at thecorresponding RE positions while muting at the remaining RE positions.

If the Rel-8 CRSs for ports 3 and 4 and the Rel-8 dedicated referencesignal for port 5 are transmitted at the RE positions of the referencesignal pattern to be muted, the Rel-8 CRSs for ports 3 and 4 aretransmitted at the REs for the Rel-8 CRSs while muting the remaining REpositions. Specifically, the dedicated reference signal for port 5 ismuted at the corresponding RE positions.

If the Rel-8 CRSs for ports 3 and 4 and the Rel-8 dedicated referencesignal for port 5 are transmitted at the RE positions of the referencesignal pattern to be muted, the Rel-8 dedicated reference signal forport 5 is transmitted at the corresponding RE positions while muting atthe remaining RE positions. Specifically, the reference signals forports 3 and 4 are muted at the corresponding RE positions.

In a conventional LTE system, the UE generates Channel QualityInformation (CQI) to be fed back in consideration of the overheadrelated to a CRS. In the LTE-A system, however, the newly introducedCSI-RS and DeModulation Reference Signal (DM-RS) can be muted.

Accordingly, if the CQI is generated in consideration of only theoverhead of the CRS as in the conventional LTE system, there is likelyto be a large difference when compared to the overhead generated in theLTE-A system. Although the enhanced Node B (eNB) can compensate for theCQI fed back from the UE in consideration of the energy loss, suchcompensation does not make up for the difference between the overheadmeasured in consideration of the energy loss and the actually appliedoverhead increases. Embodiments of the present invention remedy thisdifference through the methodology described in detail below.

When generating CQI, the UE averages the overheads of the CRS, CSI-RS,DM-RS, and muting, generates CQI in consideration of the averagedoverhead, and feeds back the CQI to the eNB.

In the LTE-A system, the various reference signals are transmitted in asubframe, and the number of reference signals can vary in differentsubframes. Accordingly, in order to calculate the number of PhysicalDownlink Shared Channel (PDSCH) REs to transmit data, it is necessary tocheck the CRS, CSI-RS, and DM-RS transmitted in each subframe, checkwhether muting is applied, and subtract the number of REs carrying thereference signals from the total number of PDSCH REs to take theoverhead into consideration. However, since the number of referencesignals change in every subframe, the UE averages the numbers of REscarrying the CRS, CSI-RS, and DM-RS, and muted, and feeds back the CQIgenerated by taking the average into consideration as the overhead tothe eNB.

In accordance with another embodiment of the present invention, muting areference signal pattern can bring a change of transmission power. If adata signal is muted, the transmission power necessary for transmittingthe data signal is saved. However, if not used by other REs, the savedtransmission power is wasted. The transmission power saved by muting thedata signal can be assigned to a RE for other data, the DM-RS signal, orthe CSI-RS. In order to allocate the transmission power saved by muting,an additional control signal is required. However, the introduction of anew control signal increases the complexity in view of the UE. In caseof the DM-RS, since the DM-RS transmission can be skipped in anyPhysical Resource Block (PRB) and the pattern of the DM-RS can bechanged according to a change of transmission rank, it is not a goodcandidate to receive the saved power.

However, the CSI-RS is transmitted periodically and the transmissioncycle of the CSI-RS is identical to that of the muting cycle. Therefore,the CSI-RS is a good candidate to receive the power saved by muting.Specifically, the transmitter can reallocate the transmission powersaved by muting a certain signal to REs carrying CSI-RS. The number ofREs reallocated the saved power is equal to the number of REs at whichthe signal is muted. The transmitter can perform this transmission powercontrol in units of OFDM symbols.

The transmission power reallocation is described in greater detailbelow. When muting is applied, the transmitter performs the transmissionpower reallocation through one of the embodiments of the presentinvention described below. The transmitter can select one of theembodiments to reallocate the saved power. Even when the transmissionpower is saved by muting, the saved power is not reallocated for theCSI-RS.

When the transmission power is saved by muting, the saved transmissionpower is reallocated for the CSI-RS. When the reference signal of theservice cell is mapped in the OFDM symbol including the muted REs, thetransmitter and the receiver assume that transmission power reallocationtakes place. The transmission power reallocation for the CSI-RS can beperformed in accordance with one of the embodiments of the presentinvention described below.

When there is no limit on transmission power for reallocation, thefollowing can be taken into account. When there are N REs to which thereference signal of the serving cell are mapped and M muted REs in anOFDM symbol (e.g., the reference signal of the serving cell has thepattern P4 of FIG. 2( a), and the muted REs has the pattern P3 of FIG.2( b)) and there is no limit on the transmission power for reallocation,the transmission power reallocated to the reference signal can beexpressed by Equation (1) below.

$\begin{matrix}{{p_{c}^{\prime} = {{10{\log \left( \frac{M + N}{N} \right)}} + p_{c}}}{p_{c} = \frac{P_{{CSI} - {RS}}}{P_{CRS}}}} & (1)\end{matrix}$

P_(CRS): transmission power for CRS

P_(CSI-RS): transmission power for CSI-RS

When there is a limit on transmission power to be reallocated, Equation(2) is utilized, as described below

$\begin{matrix}{p_{c}^{\prime} = {\min \left( {{{10{\log \left( \frac{M + N}{N} \right)}} + p_{c}},P_{\max}} \right)}} & (2)\end{matrix}$

P_(CRS): transmission power for CRS

P_(CSI-RS): transmission power for CSI-RS

P_(max): maximum transmission power of CSI-RS

When a rule is predefined for reallocating the transmission poweraccording to the number of reference signals and the number of mutedsignals (number of muted REs in the same OFDM symbol as the referencesignal), the transmission power is reallocated according to the rule.Tables 8, 9, and 10 show rules for transmission power reallocation. Inthe following tables, the reference signal patterns follow thosepatterns illustrated in FIG. 2.

TABLE 8 Number of REs of RS Number of REs of Reallocated pattern mutingpattern transmission power 2 2 ρ_(c)′ = ρ_(c) + 3 dB 4 ρ_(c)′ = ρ_(c) +4.77 dB 6 ρ_(c)′ = ρ_(c) + 6 dB 8 ρ_(c)′ = ρ_(c) + 7 dB 10 ρ_(c)′ =ρ_(c) + 7.78 dB 12 ρ_(c)′ = ρ_(c) + 8.45 dB 14 ρ_(c)′ = ρ_(c) + 9 dB 16ρ_(c)′ = ρ_(c) + 9.54 dB 18 ρ_(c)′ = ρ_(c) + 10 dB 20 ρ_(c)′ = ρ_(c) +10.4 dB 22 ρ_(c)′ = ρ_(c) + 10.8 dB 4 2 ρ_(c)′ = ρ_(c) + 1.76 dB 4ρ_(c)′ = ρ_(c) + 3 dB 6 ρ_(c)′ = ρ_(c) + 4 dB 8 ρ_(c)′ = ρ_(c) + 4.77 dB10 ρ_(c)′ = ρ_(c) + 5.44 dB 12 ρ_(c)′ = ρ_(c) + 6 dB 14 ρ_(c)′ = ρ_(c) +6.53 dB 16 ρ_(c)′ = ρ_(c) + 6.98 dB 18 ρ_(c)′ = ρ_(c) + 7.40 dB 20ρ_(c)′ = ρ_(c) + 7.78 dB 8 2 ρ_(c)′ = ρ_(c) + 0.97 dB 4 ρ_(c)′ = ρ_(c) +1.76 dB 6 ρ_(c)′ = ρ_(c) + 2.43 dB 8 ρ_(c)′ = ρ_(c) + 3.0 dB 10 ρ_(c)′ =ρ_(c) + 3.52 dB 12 ρ_(c)′ = ρ_(c) + 3.98 dB 14 ρ_(c)′ = ρ_(c) + 4.39 dB16 ρ_(c)′ = ρ_(c) + 4.77 dB

TABLE 9 Number of REs of RS Number of REs of Reallocated pattern mutingpattern transmission power 2 2 ρ_(c)′ = ρ_(c) + 3 dB 4 ρ_(c)′ = ρ_(c) +3 dB 6 ρ_(c)′ = ρ_(c) + 3 dB 8 ρ_(c)′ = ρ_(c) + 3 dB 10 ρ_(c)′ = ρ_(c) +3 dB 12 ρ_(c)′ = ρ_(c) + 3 dB 14 ρ_(c)′ = ρ_(c) + 3 dB 16 ρ_(c)′ =ρ_(c) + 3 dB 18 ρ_(c)′ = ρ_(c) + 3 dB 20 ρ_(c)′ = ρ_(c) + 3 dB 22 ρ_(c)′= ρ_(c) + 3 dB 4 2 ρ_(c)′ = ρ_(c) + 1.76 dB 4 ρ_(c)′ = ρ_(c) + 3 dB 6ρ_(c)′ = ρ_(c) + 3 dB 8 ρ_(c)′ = ρ_(c) + 3 dB 10 ρ_(c)′ = ρ_(c) + 3 dB12 ρ_(c)′ = ρ_(c) + 3 dB 14 ρ_(c)′ = ρ_(c) + 3 dB 16 ρ_(c)′ = ρ_(c) + 3dB 18 ρ_(c)′ = ρ_(c) + 3 dB 20 ρ_(c)′ = ρ_(c) + 3 dB 8 2 ρ_(c)′ =ρ_(c) + 0.97 dB 4 ρ_(c)′ = ρ_(c) + 1.76 dB 6 ρ_(c)′ = ρ_(c) + 2.43 dB 8ρ_(c)′ = ρ_(c) + 3.0 dB 10 ρ_(c)′ = ρ_(c) + 3.0 dB 12 ρ_(c)′ = ρ_(c) +3.0 dB 14 ρ_(c)′ = ρ_(c) + 3.0 dB 16 ρ_(c)′ = ρ_(c) + 3.0 dB

TABLE 10 Number of REs of RS Number of REs of Reallocated pattern mutingpattern transmission power 2 2 ρ_(c)′ = ρ_(c) + 3 dB 4 ρ_(c)′ = ρ_(c) +4.77 dB 6 ρ_(c)′ = ρ_(c) + 6 dB 8 ρ_(c)′ = ρ_(c) + 6 dB 10 ρ_(c)′ =ρ_(c) + 6 dB 12 ρ_(c)′ = ρ_(c) + 6 dB 14 ρ_(c)′ = ρ_(c) + 6 dB 16 ρ_(c)′= ρ_(c) + 6 dB 18 ρ_(c)′ = ρ_(c) + 6 dB 20 ρ_(c)′ = ρ_(c) + 6 dB 22ρ_(c)′ = ρ_(c) + 6 dB 4 2 ρ_(c)′ = ρ_(c) + 1.76 dB 4 ρ_(c)′ = ρ_(c) + 3dB 6 ρ_(c)′ = ρ_(c) + 4 dB 8 ρ_(c)′ = ρ_(c) + 4.77 dB 10 ρ_(c)′ =ρ_(c) + 5.44 dB 12 ρ_(c)′ = ρ_(c) + 6 dB 14 ρ_(c)′ = ρ_(c) + 6 dB 16ρ_(c)′ = ρ_(c) + 6 dB 18 ρ_(c)′ = ρ_(c) + 6 dB 20 ρ_(c)′ = ρ_(c) + 6 dB8 2 ρ_(c)′ = ρ_(c) + 0.97 dB 4 ρ_(c)′ = ρ_(c) + 1.76 dB 6 ρ_(c)′ =ρ_(c) + 2.43 dB 8 ρ_(c)′ = ρ_(c) + 3.0 dB 10 ρ_(c)′ = ρ_(c) + 3.52 dB 12ρ_(c)′ = ρ_(c) + 3.98 dB 14 ρ_(c)′ = ρ_(c) + 4.39 dB 16 ρ_(c)′ = ρ_(c) +4.77 dB

FIG. 4 is a diagram illustrating operations of the eNB and UE, accordingto an embodiment of the present invention.

The transmitter (i.e., eNB) determines the reference signal (i.e.,CSI-RS) pattern and muting information on the reference signal pattern(i.e., muting pattern), in step S410.

The transmitter notifies the receiver (i.e., UE) of whether referencesignal muting is applied, in step S420. If the reference signal ismuted, zero transmission power is allocated for the reference signal.

Notification of whether muting is applied is provided to the receiveraccording to the methods described above. When the REs for the CSI-RSpattern to be muted overlap with the REs to which the dedicatedreference signals or CRSs are mapped, this problem can be overcomeaccording to the methods described above. Specifically, the eNB assignsnon-zero transmission power to the REs configured for transmitting thereference signals of the corresponding cell to the UE.

The transmitter arranges the control signal and data in the subframeaccording to the reference signal pattern and according to whethermuting is applied to the reference signal pattern, in step 430. Thetransmitter performs OFDM modulation on the symbols and transmits themodulated symbols to the UE, in step S440.

The transmitter receives CQI from the UE, in step S450. The CQI isgenerated by averaging the overhead of at least one of the CRS, theCSI-RS, the DM-RS, and muting.

Meanwhile, the receiver receives the information on the reference signalpattern and muting to the reference signal pattern from the eNB, in stepS460. With this information, the receiver can check the reference signalpattern and muting to the reference signal pattern (i.e., mutingpattern).

The receiver receives the OFDM symbols transmitted by the transmitter,in step S465 and extracts the reference signal using the referencesignal pattern and the reference signal muting information acquired atstep S460. In more detail, the receiver estimates a channel using theCSI-RS among the extracted reference signal, in step S470. The receivergenerates CQI, a Rank Indicator (RI), and a Precoding Matrix Indicator(PMI) based on the estimated channel, in step S480 and feeds back theCQI, RI, and PMI to the eNB, in step S490.

The receiver performs channel estimation using the DM-RS from among theextracted reference signals, in step S475. The receiver demodulates datachannel using the estimation result, in step S485.

FIG. 5 is a block diagram illustrating a configuration of thetransmitter, according to an embodiment of the present invention. Asshown in FIG. 5, the transmitter includes a transceiver 510, memory 515,and a controller 520.

The transceiver 510 transmits the symbols of the OFDM-modulated controlsignal and data to the receiver. The transceiver 510 also receives thefeedback information, e.g., CQI, transmitted by the receiver andforwards the feedback information to the controller 520.

The memory 515 stores programs and data necessary for the operations ofthe transmitter. The memory 515 of the transmitter can store the programfor determining the reference signal pattern and generating the bitmapindicator for indicating whether the reference signal is assigned zerotransmission power in unit of a certain number of resource elements.

The controller 520 controls overall operations of the transmitteraccording to an embodiment of the present invention. Particularly, thecontroller 520 includes a reference signal pattern determiner 520A, areference signal pattern muting determiner 520B, a feedback informationprocessor 520C, and a transmission power controller 520D.

The reference signal pattern determiner 520A checks a number of antennaports used by the transmitter and determines the reference signalpattern according to the number of antenna ports. The reference signalcan be embodied as the CSI-RS. The reference signal pattern can becomposed of at least one RE. According to an embodiment of the presentinvention, the number of antenna ports can be 2, 4, or 8, and thereference signal pattern matched with the number of antennas are asdepicted in FIG. 1.

The reference signal pattern muting determiner 520B determines whetherto apply muting to the determined reference signal pattern and controlsthe process for notifying the receiver of the muting information,according to a predetermined method.

Particularly, the reference signal pattern muting determiner 520Bconfigures a muting indicator (or bitmap indicator) for indicatingwhether muting is applied to the reference signal pattern in units withat least one RE, as described above in the first embodiment of thepresent invention. The reference signal pattern muting determiner 520Bexcludes the reference signal of the serving cell so as not to be muted.In another embodiment of the present invention, the reference signalpattern muting determiner 520B can exclude the reference signal patternused for the reference signal of the serving cell in configuring themuting indicator.

As described above in the second embodiment of the present invention,the reference pattern muting determiner 520B can configure the differentreference signal patterns determined according to the number of antennaports used by the eNB in the form of tree structure. The tree structurehas branched groups that each using the same REs. A codeword is assignedto a certain node of the tree to indicate whether muting is applied. Ifa codeword of a certain node is notified to the receiver, the referencesignal pattern corresponding to the node is muted.

In more detail, according to the second embodiment of the presentinvention, all or some of the individual nodes constituting the treestructure can be assigned respective codewords.

As described in the third embodiment of the present invention, whenpositions of the Rel-8 dedicated reference signal or CRS are overlappedwith the positions of the CSI-RS to be muted, the reference signalpattern muting determiner 520B can adjust appropriately as describedabove.

The feedback information processor 520C receives the feedbackinformation transmitted by the receiver through the transceiver 510 andprocesses the feedback information. The feedback information can includeCQI, RI, and PMI. The CQI can be generated by averaging the overhead ofat least one of the CRS, CSI-RS, DM-RS, and muting.

The transmission power controller 520D can reallocate the transmissionpower saved by muting to another reference signal, particularly aCSI-RS. The transmission power reallocation method is described ingreater detail above.

FIG. 6 is a block diagram illustrating a configuration of the receiver,according to an embodiment of the present invention. As shown in FIG. 6,the receiver includes a transceiver 610, a memory 615, and a controller620.

The transceiver 610 receives the OFDM symbols carrying the controlsignal and data transmitted by the transmitter. Simultaneously, thetransceiver 610 transmits the feedback information generated by thecontroller 620 to the transmitter.

The memory 615 stores programs and data necessary for the operations ofthe receiver. The memory 615 can store the program for extracting, whenthe bitmap indicator indicating whether the reference signal is assignedzero transmission power is received, the reference signal from accordingto the received reference signal pattern and bitmap indicator andprocessing the extracted reference signal.

The controller 620 controls overall operations of the receiver accordingto an embodiment of the present invention. The controller 620 includes areference signal extractor 620A.

The reference signal extractor 620A extracts reference signals from thesubframe transmitted by the transmitter. The extracted reference signalscan include a CRS, a dedicated reference signal, a DM-RS, and a CSI-RS.Particularly, the reference signal extractor 620A can extract the CSI-RSusing the information on the reference signal pattern and whether mutingis applied to the reference signal pattern (i.e., muting pattern), whichis provided by the transmitter in advance.

In more detail, the reference signal extractor 620A controls thetransceiver 610 to receive the bitmap indicator indicating the referencesignal pattern composed of at least one RE and indicating whether the atleast one RE is assigned zero transmission power. The reference signalextractor 620A extracts and process the reference signal based on thereference signal pattern and bitmap indicator.

The reference signal extractor 620A delivers the extracted referencesignal to the channel estimator 620B.

The channel estimator 620B estimates the radio channel condition betweenthe transmitter and the receiver using the reference signal extracted bythe reference signal extractor 620A. The radio channel condition isestimated using the reference signal demodulated by the channelestimator 620B and used for demodulating a data channel (i.e., PDSCH).

The feedback information generator 620C generates the feedbackinformation to be fed back to the transmitter using the channelestimation value provided by the channel estimator 620B. The feedbackinformation can include CQI, RI, and PMI.

Particularly, the feedback information generator 620C generates the CQIby averaging the overhead of at least one of the CRS, CSI-RS, DM-RS, andmuting.

According to the above-described embodiments of the present invention,the eNB notifies the UE of the muting information on the referencesignal pattern by means of a muting indicator indicating whether thereference signal pattern is muted in units of at least one RE or acodeword allocated to a certain node of a tree structure. The UE canreceive the muting information on the reference signal pattern, extractthe reference signal from the received OFDM symbols efficiently, andperform channel estimation based on the extracted reference signal.

Also, using the UE feedback information generated by averaging theoverhead of at least one of the CRS, CSI-RS, DM-RS, and muting, the eNBcan acquire more accurate radio channel state information.

Software components including instructions or code for performing themethodologies described herein may be stored in one or more ofassociated memory devices (e.g., Read Only Memory (ROM), fixed orremovable memory) and, when ready to be utilized, loaded in part or inwhole (e.g., into Random Access Memory (RAM)) and executed by a CPU.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art various changes in form and detail may be made therein withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

What is claimed is:
 1. A method for transmitting a reference signal of abase station in a mobile communication system, comprising the steps of:determining, at the base station, a reference signal pattern comprisingat least one resource element; generating, at the base station, a bitmapindicator indicating whether zero transmission power is assigned to theat least one resource element of the reference signal pattern; andtransmitting the reference signal pattern and bitmap indicator from thebase station to a terminal.
 2. The method of claim 1, wherein generatingthe bitmap indicator comprises avoiding assignment of zero transmissionpower to resource elements to which non-zero transmission power isassigned.
 3. The method of claim 1, wherein determining the referencesignal pattern comprises selecting the reference signal patterncomprising four resource elements.
 4. The method of claim 1, whereingenerating the bitmap indicator comprises configuring the bitmapindicator by assigning the zero transmission power in units of fourresource elements.
 5. The method of claim 1, wherein the referencesignal comprises a Channel State Information Reference Signal (CSI-RS).6. A base station for transmitting reference signals in a mobilecommunication system, comprising: a reference signal pattern determinerthat determines a reference signal pattern comprising at least oneresource element; a reference signal pattern muting determiner thatgenerates a bitmap indicator indicating whether zero transmission poweris assigned to the at least one resource element of the reference signalpattern; and a transceiver that transmits the reference signal patternand the bitmap indicator to a terminal.
 7. The base station of claim 6,wherein the reference signal pattern muting determiner avoids assignmentof zero transmission power to resource elements to which non-zerotransmission power is assigned.
 8. The base station of claim 6, whereinthe reference signal pattern determiner selects the reference signalpattern comprising four resource elements.
 9. The base station of claim6, wherein the reference signal pattern muting determiner configures thebitmap indicator by assigning the zero transmission power in units offour resource elements.
 10. The base station of claim 6, wherein thereference signal comprises a Channel State Information Reference Signal(CSI-RS).
 11. A method for processing reference signals transmitted by abase station in a mobile communication system, comprising the steps of:receiving, at a terminal, a reference signal pattern from the basestation, wherein the reference signal pattern comprises at least oneresource element from the base station; receiving a bitmap indicatorindicating whether zero transmission power is assigned to the at leastone resource element of the reference signal pattern; and processing areference signal extracted according to the reference signal pattern andthe bitmap indicator.
 12. The method of claim 11, wherein processing thereference signal comprises avoiding assigning the resource elements towhich non-zero transmission power is assigned with zero transmissionpower.
 13. The method of claim 11, wherein the reference signal patterncomprises four resource elements.
 14. The method of claim 11, whereinthe bitmap indicator is configured to assign the zero transmission powerin units of four resource elements.
 15. The method of claim 11, whereinthe reference signal comprises a Channel State Information ReferenceSignal (CSI-RS).
 16. A terminal for processing reference signalstransmitted by a base station in a mobile communication system,comprising: a transceiver that communicates signals with the basestation; and a controller that controls the transceiver to receive areference signal pattern comprising at least one resource element and abitmap indicator indicating whether zero transmission power is assignedto the at least one resource element of the reference signal pattern,and that processes a reference signal extracted according to thereference signal pattern and the bitmap indicator.
 17. The terminal ofclaim 16, wherein the controller avoids assigning the resource elementsto which non-zero transmission power is assigned with zero transmissionpower.
 18. The terminal of claim 16, wherein the reference signalpattern comprises four resource elements.
 19. The terminal of claim 16,wherein the bitmap indicator is configured to assign the zerotransmission power in units of four resource elements.
 20. The terminalof claim 16, wherein the reference signal comprises a Channel StateInformation Reference Signal (CSI-RS).